Developer composition for electrophotography

ABSTRACT

A developer composition for electrophotography comprising a binding resin and a colorant, said binding resin comprising a specified nonlinear first polyester and a specified linear second polyester, the weight ratio of the first polyester to the second polyester being (80:20) to (20:80), is disclosed. 
     The developer composition of the present invention is excellent in hot offset resistance, low temperature fixation, smoothness and transparency of fixed face, and blocking resistance.

FIELD OF THE INVENTION

The present invention relates to a developer composition forelectrophotography suitable for use as a color developer for a fullcolor copying machine for developing an electrostatic charge image inelectrophotograph, electrostatic recording, electrostatic printing, etc.

DESCRIPTION OF THE RELATED ART

In electrophotography, many processes are known as described in U.S.Pat. No. 2,297,691 and Japanese Patent Publication Nos. 23910/1967 and24748/1968. Among them, a general process comprises forming anelectrical latent image on a photoreceptor by various means through theuse of a photoconductive substance, developing the latent image with atoner, optionally transferring the resultant toner image to a transfermaterial, such as paper, and fixing the image by heat, pressure orsolvent vapor to obtain a duplicate.

Various processes and apparatuses have been developed for theabove-described final step, i.e., the step of fixing a toner image on asheet, such as paper. The process most commonly used in the art at thepresent time is a press bonding heating system.

In the press bonding heating system in which a heating roller is used,the fixation is conducted by passing a fixing sheet through a heatingroller having a surface comprising a material releasable from a toner insuch a manner that the toner image on the fixing sheet is brought intocontact with the surface of the heating roller under pressure. In thisprocess, since the surface of the heating roller is brought into contactwith the toner image under pressure, the heat efficiency in the casewhere the toner image is fused to the fixing sheet is so good that thefixation can be rapidly conducted, which renders this process veryuseful in high-speed electrophotographic equipment. In theabove-described process, however, since the surface of the heatingroller comes into contact with the toner image in a molten state underpressure, part of the toner image adheres to and is transfered onto thesurface of the fixing roller and re-transfered onto the next fixingsheet, so that there occurs the so-called "offset" phenomenon which maystain the fixing sheet. The avoidance of adherence of the toner onto thesurface of the heat fixing roller is viewed as one requirement for theheat roller fixation system.

In other words, the development of a binder resin for a toner having abroad fixation temperature region and a higher offset resistance hasbeen described in the art.

Two-color copying machines and full color copying machines have alsobeen studied, and many of them have been put to practical use. Forexample, there are reports on the color reproducibility and tonerreproducibility in "Journal of the Society of the Electrophotography ofJapan", vol. 22, No. 1 page 7 (1983) and "Journal of the Society of theElectrophotography of Japan", vol. 25, No. 1, p. 52 (1986).

As opposed to television images, photographs, and color prints, the fullcolor electrophotographic image is not immediately compared with theoriginal, and full color electrophotographic images, which have been putto practical use, are not always satisfactory for persons who get usedto seeing a color image processed more beautifully than the original.

In full color electrophotography wherein development is conducted aplurality of times and it is necessary to put several kinds of tonerlayers different from each other in color on an identical substrate,color toners used in such electrophotography should satisfy thefollowing requirements.

(1) In order to avoid the inhibition of color reproducibility derivedfrom the irregular reflection of light, the fixed toner should be placedin a substantially molten state such that the form of the tonerparticles cannot be distinguished.

(2) The color toner should be transparent to such an extent that thecolor reproducibility of the underlying layer having a different colortone is not inhibited.

Thus, the toner for a full color copying machine is required to not onlyhave a broad fixation temperature region, but also have transparency andflatness in the fixed face.

In order to broaden the fixation temperature region of the polyester,Japanese Patent Laid-Open Nos. 208559/1982, 11954/1983 and 228861/1984each discloses a method in which an offset preventive agent is used. Inthese methods, however, the fluidity lowers, the toner impaction to thecarrier is accelerated in a binary system, and the transparency is lostin the case of a full color toner. Japanese Patent Laid-Open Nos.109825/1982 and 11902/1984 each discloses a method of improving theoffset resistance through the use of a polycarboxylic acid to form athree-dimensional structure in the polyester. In these methods, althoughthe offset resistance can be improved, when a large proportion isoccupied by a high molecular region, the elasticity becomes so largewhen a toner is prepared therefrom, so that the fixed face does notbecome flat when the fixation is conducted at relatively lowtemperature. This brings about the problem of color reproducibility whenit is used in a full color toner. Further, Japanese Patent Laid-OpenNos. 7960/1984, 9669/1984 and 29255-29258/1984 each discloses a methodof forming a three-dimensional structure in the polyester through theuse of a tricarboxylic or higher polycarboxylic acid or a triol or ahigher polyol. In the methods described in Japanese Patent Laid-OpenNos. 29255 and 29256/1984, however, the fixation is poor due to theabsence of a soft segment, such as a succinic acid derivative. Further,in the methods described in Japanese Patent Laid-Open Nos. 7960/1984,9669/1984, 29257/1984 and 29258/1984, since succinic acid substitutedwith an alkyl group is used, the toner exhibits fixation superior tothat of the toners disclosed in Japanese Patent Laid-Open Nos. 29255 and29256/1984 but is still unsatisfactory in fixation when it is used in afull color toner.

As described above, it is very difficult to simultaneously satisfy thebroadening of the fixation temperature region and the toner properties,i.e., charging properties, fluidity, durability, transparency andsmoothness of the fixed face.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a novel developercomposition for electrophotography which eliminates the above-describedproblems.

Another object of the present invention is to provide a developercomposition for electrophotography comprising a toner for heat rollerfixation capable of forming a smooth fixed face for the purpose ofavoiding the inhibition of color reproduction derived from irregularreflection.

A further object of the present invention is to provide a developercomposition for electrophotography comprising a toner for heat rollerfixation which has excellent fluidity, no agglomeration, and hasexcellent impact resistance.

Further scope of the apllicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

The present inventors have made intensive studies with a view towardattaining the above-described objects and, as a result, have completedthe present invention.

Specifically, the present invention relates to a developer compositionfor electrophotography comprising a binding resin and a colorant, saidbinding resin comprising a first polyester and a second polyester, theweight ratio of the first polyester to the second polyester being(80:20) to (20:80), said first polyester being a nonlinear polyestercomprising an acid component (A) derived from an aliphatic dicarboxylicacid and/or acid anhydride thereof in an amount of 50% and or more bymole based on the entire acid component, and an acid component (B)derived from a compound selected from the group consisting of atricarboxylic acid, a higher polycarboxylic acid, an acid anhydridethereof and a lower alkyl ester thereof in an amount from 0.05% by moleto 40% by mole exclusively based on the entire acid component and/or analcohol component (A) derived from a triol and/or a higher polyol in anamount from 0.05% by mole to 40% by mole exclusively based on the entirealcohol component, and having a softening point, Tsp, in the range offrom 100° C. to 130° C. exclusive, said second polyester being a linearpolyester comprising an acid component (C) derived from an aliphaticdicarboxylic acid and/or an acid anhydride thereof in an amount of 50%or more by mole based on the entire acid component, and having asoftening point, Tsp, in the range of from 80° C. to 110° C. exclusiveyand lower than that of the first polyester by at least 10° C.

It is preferable that the first polyester and the second polyester eachfurther comprises an alcohol component (B) derived from a compoundrepresented by the following general formula (1) as a main component ofthe alcohol component originated from a diol, ##STR1## wherein Rrepresents an ethylene group or a propylene group and x and y are eachan integer, provided that the average value of the sum of x and y valuesis 2 to 7.

Furthermore, it is preferable that the glass transition temperature ofthe first polyester and the second polyester each is 40° to 80° C.

The first polyester preferably has 0 to 5% by weight of chloroforminsoluble matter.

The binding resin preferably 70 to 100% by weight of the total amount ofthe first polyester and the second polyester based on the entire bindingresin.

The binding resin more preferably comprises 70 to 100% by weight of thetotal amount of the first polyester, and the second polyester and 30 to0% by weight of styrene-acrylic resin based on the entire binding resin.

The developer composition of the present invention further comprises alow molecular weight polyolefin and/or a magnetic impalpable powder,preferably.

DETAILED DESCRIPTION OF THE INVENTION

The constitution of the present invention will now be described indetail. In the above-described first polyester, when the proportion ofthe component derived from the trivalent and higher monomer based on theentire monomer, that is, each of the proportion of the acid component(B) based on the entire acid component and the proportion of the alcoholcomponent (A) derived from a triol and/or a higher polyol based on theentire alcohol component, is larger than the above-described range andthe softening point, Tsp, is higher than the above-described range, thelow temperature fixation and the smoothness of the fixed face becomelower. On the other hand, when the proportion of the trivalent andhigher monomer based on the entire monomer is smaller than theabove-described range and the softening point, Tsp, is lower than theabove-described range, the hot offset resistance becomes lower.

In the above-described second polyester, when the softening point, Tsp,is higher than the above-described range, the low-temperature fixationand the smoothness of the fixed face become lower, while when thesoftening point, Tsp, is lower than the above-described range, the hotoffset resistance and the blocking resistance become lower.

Basically, when the difference in the softening point, Tsp, between theabove-described first polyester and the above-described second polyestercontained in the developer composition of the present invention is 10°C. and more, excellent properties of the individual polyesters areexhibited. On the other hand, when the difference in the softeningpoint, Tsp, is less than 10° C., the expression of the excellentproperties of each of the first polyester and the second polyester issuppressed, such that some of the properties, among those of hot offsetresistance, low temperature fixation, transparency, smoothness of thefixed face and blocking resistance, are adversely affected.

Further, in the above-described first polyester, the chloroforminsoluble matter is preferably 0 to 5% by weight. When the chloroforminsoluble matter exceeds 5% by weight, the low temperature fixation,smoothness of fixed face and transparency are liable to become lower.

The blending weight ratio of the above-described first polyester to theabove-described second polyester is (80:20) to (20:80), particularlypreferably (70:30) to (30:70). When the blending weight ratio of theabove-described first polyester is higher than the above-describedrange, the low temperature fixation and the smoothness of the fixed faceare liable to be reduced. On the other hand, when the blending weightratio of the first polyester is lower than the above-described range,the hot offset resistance and the blocking resistance are liable to bereduced.

The proportion of the acid component (A) in the above-described firstpolyester and the proportion of the acid component (C) in theabove-described second polyester are 50% or more by mole based on theentire acid component, respectively. When the proportion of the acidcomponents (A) and (C), derived from an aliphatic dicarboxylic acidand/or acid anhydride thereof and being a relatively soft segment, fallwithin the above-described range, the low temperature fixation, thesmoothness of the fixed face and the transparency become better.

It is preferred that the first polyester and the second polyester eachfurther comprises an alcohol component (B) derived from a diolrepresented by the following general formula (1) as a main component ofthe alcohol component derived from a diol: ##STR2## wherein R representsan ethylene group or a propylene group, and x and y are each an integer,provided that the average value of the sum of x and y values is 2 to 7.

The presence of the above-described component (B) derived from the diolas the constituent unit contributes to a further improvement in the hotoffset resistance, low temperature fixation and blocking resistance ofthe toner.

The glass transition point, Tg, of the above-described first and secondpolyesters each is preferably 40° to 80° C. A further improvement in thehot offset resistance, low temperature fixation and blocking resistancecan be attained through the selection of polyesters having a glasstransition point falling within the above-described range. Specifically,when the glass transition point, Tg, is higher than the above-describedrange, the low temperature fixation and the smoothness of the fixed faceare liable to be lower. On the other hand, when the glass transitionpoint, Tg, is lower than the above-described range, the blockingresistance is liable to be lower.

In the present invention, examples of the monomer used for the synthesisof the first polyester basically include the following monomers (i) and(ii), and examples of the monomer used for the synthesis of the secondpolyester basically include the following monomer (i). If necessary,they may be used in combination with other monomers.

(i) Diol monomers and dicarboxylic acid monomers as a compound forconstituting the basic skeleton, that is, the main chain of thepolyester.

(ii) Triol or higher polyol monomers and/or tricarboxylic or higherpolycarboxylic acid monomers which participate in the non-linearization,that is, branching or reticulation of the polyester.

Examples of the diol monomer described in the above item (i) includeetherified bisphenol, ethylene glycol, diethylene glycol, triethyleneglycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol,neopentyl glycol, 1,4-butenediol, 1,5-pentanediol, 1,6-hexanediol,1,4-cyclohexanedimethanol, dipropylene glycol, polyethylene glycol,polypropylene glycol, polytetramethylene glycol, bisphenol A andhydrogenated bisphenol A.

Among them, etherified bisphenol is particularly effective. Specificexamples thereof include polyoxypropylene(2.2)-2,2-bis(4-hydroxyphenyl)propane, polyoxypropylene(3.3)-2,2-bis(4-hydroxyphenyl)propane,polyoxyethylene(2.0)-2,2-bis(4-hydroxyphenyl)propane,polypropylene(2.0)-polyoxyethylene(2.0)-2,2-bis(4-hydroxyphenyl)propaneand polyoxypropylene(6)-2,2-bis(4-hydroxyphenyl)propane.

Preferred examples of the dicarboxylic acid monomer described in theabove-described item (i) include aliphatic dicarboxylic acids such asmaleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconicacid, succinic acid, adipic acid, sebacic acid, azelaic acid, malonicacid, n-dodecenylsuccinic acid, isododecenylsuccinic acid,n-dodecylsuccinic acid, isododecyl succinic acid, n-octenylsuccinicacid, n-octylsuccinic acid and anhydrides or lower alkyl esters of theseacids. If necessary, it is also possible to use aromatic dicarboxylicacids such as phthalic acid, isophthalic acid, terephthalic acid andanhydrides and lower alkyl esters of the above-described acids.

Examples of the triol or higher polyol monomer described in the aboveitem (ii) include sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan,pentaerythritol, dipentaerythritol, tripentaerythritol,1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, 2-methylpropanetriol,2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane and1,3,5-trihydroxymethylbenzene.

Examples of the tricarboxylic or higher polycarboxylic acid monomerdescribed in the above-described item (ii) include1,2,4-benzenetricarboxylic acid, 2,5,7-naphthalenetricarboxylic acid,1,2,4-naphthalenetricarboxylic acid, 1,2,4-butanetricarboxylic acid,1,2,5-hexanetricarboxylic acid,1,3-dicarboxyl-2-methyl-2-methylenecarboxypropane,1,2,4-cyclohexanetricarboxylic acid, tetra(methylenecarboxyl)methane,1,2,7,8-octanetetracarboxylic acid, pyromellitic acid, enpole trimeracid and anhydrides or lower alkyl esters of these acids.

In the present invention, the softening point, Tsp, and the glasstransition point, Tg, are defined respectively as values measured by thefollowing methods.

Softening Point, Tsp

The softening point is defined as a temperature corresponding to 1/2 ofthe height from the flow initiation point to the flow termination pointin the case where a sample having an area of 1 cm² is melt-flowed underconditions of a die pore diameter of 1 mm, a pressure of 20 kg/cm² and atemperature rise rate of 6° C./min through the use of a Koka flow tester"CFT-500" (manufactured by Shimadzu Corporation).

Glass Transition Point, Tg

A sample is heated to 100° C. by means of a differential scanningcalorimeter (manufactured by Seiko Instruments Inc.), maintained at thattemperature for 3 min and then cooled to room temperature at atemperature reducing rate of 10° C./min. In this sample, the measurementis conducted at a temperature increase of 10° C./min to obtain a curve.The intersection of a line extending from the base line of the curve ata portion below the glass transition temperature and a tangential linehaving the maximum gradient between the rising portion of the peak andthe vertex of the peak is determined, and the temperature at thatintersection is defined as the glass transition temperature, Tg.

In the present invention, the chloroform insoluble matter is the contentof matter incapable of passing through a filter paper when a sample isdissolved in chloroform, and can be determined by the following method.

5.00 g of a sample powder obtained by finely grinding a sample andpassing the powder through a 40 mesh sieve is placed in a containerhaving a capacity of 150 ml together with 5.00 g of radiolite (#700) asa filter aid. 100 g of chloroform are poured into the container, and thecontainer is put on a ball mill frame and rotated over 5 hours or longerto sufficiently dissolve the sample in chloroform. A filter paper havinga diameter of 7 cm (No. 2) is put within a pressure filter and evenlypre-coated with 5.00 g of radiolite. A small amount of chloroform isadded to the filtration paper, the filtration paper is brought intocontact with the filter, the contents of the above-described containerare poured into the filter, and the container is thoroughly washed with100 ml of chloroform which is then poured into the filter so that thedeposit does not remain on the wall of the container. Thereafter, theupper lid of the filter is closed, and the filtration is conducted. Thefiltration is conducted under a pressure of 4 kg/cm² or less. After theoutflow of chloroform stops, 100 ml of fresh chloroform are added towash the residue on the filtration paper and the filtration is conductedagain under pressure.

After the completion of the above-described procedure, all thefiltration paper, the residue on the filtration paper and the radioliteare put on an aluminum foil, placed in a vacuum drier, and dried at atemperature of 80° to 100° C. and a pressure of 100 mmHg for 10 hours.The total weight, a (g), of the dried matter thus obtained is measured,and the chloroform insoluble matter, X (% by weight), is determined bythe following equation: ##EQU1##

In polyester, the chloroform insoluble matter thus determined is a highmolecular weight polymer component or a cross-linked polymer component.

The developer composition of the present invention contains theabove-described first polyester and the above-described second polyesteras indispensable components. The first polyester and the secondpolyester may be previously melt-blended with each other. The developercomposition further contains a colorant, and, if necessary, may containthe other additives and resins besides first and second polyesters.

Low molecular weight polyolefins can be preferably used as the otheradditives. Specifically, low molecular weight polyethylene andpolypropylene, etc., may be preferably used, and the softening pointthereof as determined by the ring-and ball method is preferably 70° to150° C., further advantageously 120° to 150° C. The incorporation of theabove-described low molecular weight polyolefin contributes to furtherimprovement in the hot offset resistance.

Examples of the above-described colorant include carbon black, nigrosinedyes (C. I. No. 50415B), aniline blue (C. I. No. 50405), chalco oil blue(C. I. No. azoic Blue 3), chrome yellow (C. I. No. 14090), ultramarineblue (C. I. No. 77103), de Pont oil red (C. I. No. 26105), quinolineyellow (C. I. No. 47005), methylene blue chloride (C. I. No. 52015),phthalocyanine blue (C. I. No. 74160), malachite green oxalate (C. I.No. 42000), lamp black (C. I. No. 77266), rose bengal (C. I. No. 45435)and a mixture thereof. In general, the content of these colorants ispreferably about 1 to 20 parts by weight based on 100 parts by weight ofthe toner.

The toner according to the present invention can be prepared, forexample, by the following method. Specifically, a toner comprising apowder having a desired particle diameter can be prepared by adding acolorant(s) to the mixture of the first polyester and the secondpolyester and optionally other resin(s), preliminarily mixing them witheach other, melt-kneading the mixture and subjecting the kneaded mixtureto cooling, granulation, pulverization and classification.

In the present invention, although there is no particular limitation onthe particle diameter of the toner, the mean particle size is usually 3to 30 μm.

If necessary, flow improvers, cleaning improvers, etc. may beincorporated into the toner according to the present invention. Examplesof the flow improver include silica, alumina, titanium oxide, bariumtitanate, magnesium titanate, calcium titanate, strontium titanate, zincoxide, quartz sand, clay, mica, wollastonite, diatomaceous earth,chromium oxide, cerium oxide, red iron oxide, antimony trioxide,magnesium oxide, zirconium oxide, barium sulfate, barium carbonate,calcium carbonate, silicon carbide and silicon nitride. Impalpablepowder of silica is particularly preferred.

The impalpable powder of silica is a fine powder of a compound having aSi--O--Si bond, and may be prepared either the dry process or the wetprocess. Although the impalpable powder may be any of aluminum silicate,sodium silicate, potassium silicate, magnesium silicate and zincsilicate as well as anhydrous silicon dioxide, the impalpable powdercontaining 85 to 100% by weight of SiO₂ is preferable. It is alsopossible to use an impalpable powder of silica subjected to a surfacetreatment with a silane coupling agent, a titanium coupling agent, asilicone oil, a silicone oil having an amine in its side chain and thelike in the present invention.

Examples of the cleaning improver include impalpable or fine powders ofmetal salts of higher fatty acids represented by zinc stearate andfluoropolymers.

Further, it is also possible to use additives for adjusting thedevelopability, for example, an impalpable powder of a polymer of methylmethacrylate.

Further, a minor amount of carbon black may be used for the purpose ofadjusting the color tone and resistance. Examples of the carbon blackuseable in the present invention include various types of carbon blackknown in the art, for example, furnace black, channel black andacetylene black.

When the toner according to the present invention contains a magneticimpalpable or fine powder, it may be used alone as a developer. On theother hand, when it contains no magnetic impalpable powder, it may beused in the form of a binary developer prepared by mixing it with acarrier. There is no particular limitation on the carrier, and examplesthereof include iron powder, ferrite and glass beads or theabove-described carriers coated with a resin. The mixing ratio of thetoner to the carrier is 0.5 to 10% by weight. The particle diameter ofthe carrier is 30 to 500 μm. It is also possible to use a nonmagneticone-component toner without the use of a carrier.

Since the developer composition of the present invention comprises firstand second polyesters, each having particular properties, it isexcellent in hot offset resistance, low temperature fixation, smoothnessand transparency of the fixed face and blocking resistance by virtue ofa synergistic effect between these first and second polyesters.

Specifically, the first polyester is a nonlinear polyester containing anacid component (B) and/or an alcohol component (A) derived from atrivalent or higher monomer and has a relatively high molecular weight.The first polyester, as such, is excellent in hot offset resistance andblocking resistance. However, it causes deterioration in the surfacesmoothness in the low temperature fixation region. On the other hand,the second polyester is a linear polyester having a relatively lowmolecular weight. As such, it imparts excellent low temperature fixationand smoothness of the fixed face. However, it causes deterioration inthe hot offset resistance and blocking resistance. Therefore, when thefirst polyester and the second polyester are used alone, the respectivedrawbacks are remarkably exhibited. However, in the developercomposition of the present invention, since both the first polyester andthe second polyester are present together, the mixture contains theso-called "linearly broadened molecular weight distribution". As aresult, the toner according to the present invention is excellent in hotoffset resistance and blocking resistance by virtue of the presence ofthe first polyester having a relatively high molecular weight, and, atthe same time, exhibits excellent low temperature fixation andsmoothness of the fixed face by virtue of the presence of the secondpolyester having a low molecular weight, so that it is possible toattain excellent results whereby low temperature fixation and thesmoothness of the fixed face can be significantly improved withoutadversely affecting the hot offset resistance, and blocking resistanceand furthermore, a toner having excellent properties can be efficientlyprepared by the conventional kneading-pulverization process.

EXAMPLES

The present invention will now be described in more detail withreference to the following Examples which should not be considered tolimit the scope of the present invention.

Production of Polyester

A four neck flask having a capacity of 2 liters and equipped with athermometer, a stainless steel agitator, a glass nitrogen inlet tube anda falling condenser was charged with components according to theformulation indicated in Table 1 with the further addition of 0.75 g ofhydroquinone, and then set in a mantle heater. The contents of the flaskwere allowed to react with each other at 220° C. and below in a nitrogenatmosphere and under reduced pressure with agitation. The progress ofthe reaction was monitored by measuring the acid value, and the reactionwas stopped when the acid value reached a predetermined value. The flaskwas then cooled to room temperature to produce individual polyester as ayellow solid form.

The property values of the respective polyesters are given in Table 2.

                                      TABLE 1                                     __________________________________________________________________________    Monomer for Alcohol Component                                                 polyoxy-                Monomer for Acid Component                                 propylene                          1,2,4-                                     (2.2)-2,2-                                                                          polyoxy-                     benzene                                    bis(4-                                                                              ethylene(2.0)-    iso-       tri-                                       hydroxy-                                                                            2,2-bis(4-                                                                            tri-      dodecenyl                                                                           iso- carboxylic                            Polyester                                                                          phenyl)                                                                             hydroxyphenyl)                                                                        methylol-                                                                          fumaric                                                                            succinic                                                                            phthalic                                                                           acid                                  No.  propane                                                                             propane propane                                                                            acid anhydride                                                                           acid anhydride                             __________________________________________________________________________    1-1  1050 g                                                                              --      --   313 g                                                                              --    --    58 g                                      (3.0 mol)          (2.7 mol)       (0.3 mol)                             1-2a 1050 g                                                                              --      --   278 g                                                                              --    --   115 g                                      (3.0 mol)          (2.4 mol)       (0.6 mol)                             1-2b 1050 g                                                                              --      --   278 g                                                                              --    --   115 g                                      (3.0 mol)          (2.4 mol)       (0.6 mol)                             1-2c 1050 g                                                                              --      --   278 g                                                                              --    --   115 g                                      (3.0 mol)          (2.4 mol)       (0.6 mol)                             1-3  1050 g                                                                              --      --   174 g                                                                              --    --   288 g                                      (3.0 mol)          (1.5 mol)       (1.5 mol)                             2-1  1050 g                                                                              --      --   244 g                                                                               80 g --   115 g                                      (3.0 mol)          (2.1 mol)                                                                          (0.3 mol)  (0.6 mol)                             3-1  1050 g                                                                              --      --   104 g                                                                              161 g 100 g                                                                              173 g                                      (3.0 mol)          (0.9 mol)                                                                          (0.6 mol)                                                                           (0.6 mol)                                                                          (0.9 mol)                             4-1   735 g                                                                              293 g   --   244 g                                                                              --    100 g                                                                              58 g                                       (2.1 mol)                                                                           (0.9 mol)    (2.1 mol)  (0.6 mol)                                                                          (0.3 mol)                             5-1a  945 g                                                                              --      40 g 348 g                                                                              --    --   --                                         (2.7 mol)     (0.3 mol)                                                                          (3.0 mol)                                             5-1b  945 g                                                                              --      40 g 348 g                                                                              --    --   --                                         (2.7 mol)     (0.3 mol)                                                                          (3.0 mol)                                             6-1a 1050 g                                                                              --      --   348 g                                                                              --    --   --                                         (3.0 mol)          (3.0 mol)                                             6-1b 1050 g                                                                              --      --   348 g                                                                              --    --   --                                         (3.0 mol)          (3.0 mol)                                             6-1c 1050 g                                                                              --      --   348 g                                                                              --    --   --                                         (3.0 mol)          (3.0 mol)                                             7-1  1050 g                                                                              --      --   278 g                                                                              --    100 g                                                                              --                                         (3.0 mol)          (2.4 mol)  (0.6 mol)                                  __________________________________________________________________________

                  TABLE 2                                                         ______________________________________                                               Proportion of                                                                 the component                                                                 originated from                                                               trivalent or                                                                  higher monomer           Glass  Choro-                                        based on the             tran-  form                                          entire acid component    sition in-                                    Polyester                                                                            or the entire   Softening                                                                              point  soluble                                No.    alcohol component                                                                             point Tsp                                                                              Tg     matter                                 ______________________________________                                        1-1    10 mol. %       114° C.                                                                         64° C.                                                                         0%                                    1-2a   20               95      58      0                                     1-2b   20              116      65      0                                     1-2c   20              135      68     14.2                                   1-3    50              123      67      0.9                                   2-1    20              110      63      0                                     3-1    30              113      65      0                                     4-1    10              114      60      0                                     5-1a   10              104      58      0                                     5-1b   10              115      60      0                                     6-1a    0               85      52      0                                     6-1b    0              102      59      0                                     6-1c    0              115      65      0                                     7-1     0               92      57      0                                     ______________________________________                                    

EXAMPLES 1 TO 7 AND COMPARATIVE EXAMPLES 1 TO 7

In the individual Examples and Comparative Examples, 80 parts by weightin total of the polyesters in combination and blended in the amountindicated in Table 3, 20 parts by weight of styrene-acrylic resin, 1part by weight of a magenta dye "ROB-B" (manufactured by Orient ChemicalIndustries, Ltd.), 0.8 part by weight of a charge control agent "BontronP-51" (manufactured by Orient Chemical Industries, Ltd.), and 2 parts byweight of a low molecular weight polypropylene "Viscol 660P" (softeningpoint, Tsp, 130° C.; a product of Sanyo Chemical Industries, Ltd.) werepreliminarily mixed with each other. Then the resulting mixture wassubjected to conventional procedures, i.e., melting, kneading, cooling,grinding and classification, to prepare a particulate powder having aparticle diameter of 10 μm.

In the step of grinding, the mass after kneading, was crushed andclassified to pass a 9.2 mesh (nominal size: 2 mm)/16 mesh on (nominalsize: 1 mm) and finely ground by means of a jet fine grinding mill. 0.3part by weight of an impalpable powder of hydrophobic silica "AerosilR-972" was added and mixed with 100 parts by weight of the particulatepowder to give a toner according to the present invention.

50 parts by weight of the toner thus obtained was mixed with 950 partsby weight of silicone-coated ferrite carrier (manufactured by KantoDenka Kogyo Co., Ltd.) by means of a V-shape blender to give adeveloper.

This developer was used in a two-component dry copying machine equippedwith a commercially available organic photoreceptor to obtain an initialimage and subjected to a performance evaluation according to thefollowing methods.

EVALUATION METHODS (1) Minimum Fixation Temperature

An unfixed image was formed within a copying machine, and a test wasconducted on a fixation temperature region by means of an externalfixing machine. In the fixing roller of the external fixing machine,both the upper and lower rollers were coated with a high heat resistantsilicone rubber, and a heater was provided within the upper roller.

Toner images formed by the above-described individual toners transferredon a transfer paper having a basis weight of 64 g/m² under environmentalconditions of a temperature of 20° C. and a relative humidity of 20%were fixed at a linear velocity of 115 mm/sec by means of a heat rollerfixing apparatus which was conducted by the stepwise raising of the settemperature of the heat roller from 120° C.

In the resultant fixed image, a solid toner having a size of 2 cm×2 cmwas folded in two, and the folded portion was inspected with the nakedeye to determine whether the toner was fixed or not. The minimum presettemperature necessary for obtaining a fixed image was determined. Thistemperature was viewed as the minimum fixing temperature. The heatroller fixing apparatus is one not equipped with a silicone oil feedmechanism.

(2) Hot Offset Generation Temperature

According to the above-described measurement of the minimum fixingtemperature, a toner image was transferred, a fixation treatment wasconducted by means of the above-described heat roller fixing apparatus,and a transfer paper having a white color was fed to the above-describedheat roller fixing apparatus under the same conditions to determine withthe naked eye whether or not toner staining occurred. Theabove-described procedure was repeated in such a manner that the presettemperture of the heat roller of the above-described heat roller fixingapparatus was successively raised, thereby determining the minimumpreset temperature at which the toner staining occurred. The minimumpresent temperature was viewed as the hot offset generation temperature.

(3) Gloss of Fixed Face

At a coverage of 15 mg/cm² of the toner on the paper, the gloss of thetoner image which formed by fixing at each fixing temperature wasmeasured through the use of a glossmeter "MODEL VG-2PD" manufactured byNippon Denshoku Co., Ltd.

The results are summarized in Table 3.

                                      TABLE 3                                     __________________________________________________________________________               propor-                                                                       tion of                                                                       the com-                                                                      ponent                                                                        origi-           proportion                                                   nated from       of the                                                       trivalent        component                                                    or higher        originated                                                   monomer          from trivalent                                               based            or higher                                                    on the           monomer                                                      entire acid      based on the                                                 component        entire acid                                                  or the                                                                              soften-                                                                           amt.   component or                                                                         soften-                                                                           amt.                                                                              Offset                                        entire                                                                              ing of     the entire                                                                           ing of  genera-                                                                           Min.                           Toner      alcohol                                                                             point                                                                             blend- alcohol                                                                              point                                                                             blen-                                                                             tion                                                                              fixation                                                                          Gloss                      No.     No.                                                                              component                                                                           Tsp ing No.                                                                              component                                                                            Tsp ding                                                                              temp.                                                                             temp.                                                                             160° C.                                                                    180°                                                                       200°        __________________________________________________________________________                                                               C.                 Ex. 1                                                                             toner 1                                                                           1-1                                                                              10.0  114° C.                                                                    60  6-1b                                                                             0 mol. %                                                                             102° C.                                                                    40  210° C.                                                                    160° C.                                                                    7   13  26                            mol. %    pts.              pts.                                                        wt                wt                                     Ex. 2                                                                             toner 2                                                                           1-2b                                                                             20.0  116 60  6-1b                                                                             0      102 40  220 160 6   11  20                 Ex. 3                                                                             toner 3                                                                           2-1                                                                              20.0  110 60  6-1a                                                                             0       85 40  210 150 9   16  29                 Ex. 4                                                                             toner 4                                                                           2-1                                                                              20.0  110 60  7-1                                                                              0       92 40  210 150 10  16  28                 Ex. 5                                                                             toner 5                                                                           3-1                                                                              30.0  113 40  6-1a                                                                             0       85 60  210 150 9   15  28                 Ex. 6                                                                             toner 6                                                                           4-1                                                                              10.0  114 40  6-1b                                                                             0      102 60  210 160 6   10  20                 Ex. 7                                                                             toner 7                                                                           5-1b                                                                             10.0  115 30  6-1a                                                                             0       85 70  210 150 11  18  29                 Comp.                                                                             comp.                                                                             1-2a                                                                             20.0   95° C.                                                                    60  6-1b                                                                             0 mol. %                                                                             102 40  160 150 --  --  --                 Ex. 1                                                                             toner 1                                                                              mol. %    pts.              pts.                                                        wt                wt                                     Comp.                                                                             comp.                                                                             1-2c                                                                             20.0  135 60  6-1b                                                                             0      102 40  230 170 --   7  10                 Ex. 2                                                                             toner 2                                                                   Comp.                                                                             comp.                                                                             1-3                                                                              50.0  123 60  6-1b                                                                             0      102 40  230 170 --   6  11                 Ex. 3                                                                             toner 3                                                                   Comp.                                                                             comp.                                                                             1-2b                                                                             20.0  116 60  6-1c                                                                             0      115 40  220 170 --   8  12                 Ex. 4                                                                             toner 4                                                                   Comp.                                                                             comp.                                                                             1-2b                                                                             20.0  116 100 -- --     --  --  220 170 --   7  11                 Ex. 5                                                                             toner 5                                                                   Comp.                                                                             comp.                                                                             -- --    --  --  6-1b                                                                             0      102 100 170 150 8   --  --                 Ex. 6                                                                             toner 6                                                                   Comp.                                                                             comp.                                                                             5-1a                                                                             10.0  104 60  6-1b                                                                             0      102 40  170 150 8   --  --                 Ex. 7                                                                             toner 7                                                                   __________________________________________________________________________

Further, the above-described toners 1 to 7 were allowed to stand underenvironmental conditions at a temperature of 45° C. and a relativehumidity of 26% for 2 weeks, and the blocking resistance was evaluatedbased on whether or not agglomeration occurs in each toner. As a result,no agglomerate was observed, and the blocking resistance was excellent.

As can be understood from the above-described results, all the toners 1to 7 of the present invention were excellent in hot offset resistance,low temperature fixation, gloss of fixed face and blocking resistance,and it is possible to prepare a toner which is excellent particularly inits heat characteristics.

By contrast, the comparative toner 1 is poor in hot offset resistancebecause the softening point, Tsp, of the first polyester is below 100°C.

The comparative toner 2 is poor in low temperature fixation and gloss offixed surface because the softening point, Tsp, of the first polyesteris not below 130° C.

The comparative toner 3 is poor in low temperature fixation and glossbecause the proportion of use of the trivalent or higher monomer is 40%by mole or more in the production of the first polyester.

The comparative toner 4 is poor in low temperature fixation and glossbecause the softening point, Tsp, of the second polyester is not below110° C.

The comparative toner 5 is poor in low temperature fixation and glossbecause it contains no second polyester.

The comparative toner 6 is poor in hot offset resistance because itcontains no first polyester.

The comparative toner 7 is poor in hot offset resistance because thedifference in the softening point, Tsp, between the first polyester andthe second polyester is less than 10° C.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and acope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

What we claim:
 1. A developer composition for electrophotography,comprising a binding resin and a colorant,said binding resin comprisinga first polyester and a second polyester, the weight ratio of said firstpolyester to said second polyester being 80:20 to 20:80, said firstpolyester being a nonlinear polyester comprising an acid component (A)derived from an aliphatic dicarboxylic acid and/or an acid anhydridethereof in an amount of 50% or more by mole based on the entire acidcomponent, and an acid component (B) derived from a compound selectedfrom the group consisting of a tricarboxylic acid, a higherpolycarboxylic acid, an acid anhydride thereof, and a lower alkyl esterthereof in an amount from 0.05% by mole to 40% by mole exclusively basedon the entire acid component and/or an alcohol component (A) derivedfrom a triol and/or a higher polyol in an amount from 0.05% by mole to40% by mole exclusively based on the entire alcohol component, andhaving a softening point, Tsp, in the range of from 100° C. to 130° C.exclusively, said second polyester being a linear polyester comprisingan acid component (C) derived from an aliphatic dicarboxylic acid and/oran acid anhydride thereof in an amount of 50% or more by mole based onthe entire acid component, and having a softening point, Tsp, in therange of from 80° C. to 110° C. exclusively and lower than that of thefirst polyester by at least 10° C.
 2. The developer composition forelectrophotography according to claim 1, wherein said first polyesterand said second polyester each comprises an alcohol component (B)derived from a compound represented by the following general formula (1)as a main component of the alcohol component derived from a diol:##STR3## wherein R represents an ethylene group or a propylene group,and x and y are each an integer, provided that the average value of thesum of x and y values is 2 to
 7. 3. The developer composition forelectrophotography according to claim 1, wherein the glass transitiontemperature of said first polyester and said second polyester each is40° to 80° C.
 4. The developer composition for electrophotographyaccording to claim 1, wherein said first polyester contains 0 to 5% byweight of chloroform insoluble matter.
 5. The developer composition forelectrophotography according to claim 1, wherein said binding resincomprises 70 to 100% by weight of the total amount of said firstpolyester and the second polyester based on said entire binding resin.6. The developer composition for electrophotography according to claim1, wherein said binding resin comprises 70 to 100% by weight of thetotal amount of said first polyester and said second polyester and 30 to0% by weight of styrene-acrylic resin based on the entire binding resin.7. The developer composition for electrophotography according to claim1, wherein said developer composition further comprises a low molecularweight polyolefin.
 8. The developer composition for electrophotographyaccording to claim 1, wherein said developer composition furthercomprises a magnetic impalpable powder.
 9. The developer compositionaccording to claim 1, wherein the weight ratio of said first polyesterto said second polyester is 70:30 to 30:70.
 10. The developercomposition according to claim 1, wherein said first polyester issynthesized from at least one monomer selected from the group consistingof a diol monomer, a dicarboxylic acid monomer, a triol monomer, ahigher polyol monomer, a tricarboxylic acid monomer, and a higherpolycarboxylic acid monomer, and said second polyester is synthesizedfrom at least one monomer selected from the group consisting of a diolmonomer and a dicarboxylic acid monomer.
 11. The developer compositionaccording to claim 10, wherein said diol monomer is a member selectedfrom the group consisting of etherified bisphenol, ethylene glycol,diethylene glycol, triethylene glycol, 1,2-propylene glycol,1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, 1,4-butenediol,1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, dipropyleneglycol, polyethylene glycol, polypropylene glycol, polytetramethyleneglycol, bisphenol A and hydrogenated bisphenol A.
 12. The developercomposition according to claim 11, wherein said etherified bisphenol isa member selected from the group consisting of polyoxypropylene(2.2)-2,2-bis(4-hydroxyphenyl)propane, polyoxypropylene(3.3)-2,2-bis(4-hydroxyphenyl) propane, polyoxyethylene(2.0)-2,2-bis(4-hydroxyphenyl) propane, polypropylene(2.0)-polyoxyethylene(2.0)-2,2-bis(4-hydroxyphenyl) propane andpolyoxypropylene (6)-2,2-bis(4-hydroxyphenyl) propane.
 13. The developercomposition according to claim 10, wherein said dicarboxylic acidmonomer is a member selected from the group consisting of an aliphaticdicarboxylic acid, an anhydride or an aliphatic dicarboxylic acid, alower alkyl ester of an aliphatic dicarboxylic acid, an aromaticdicarboxylic acid, an anhydride of an aromatic dicarboxylic acid, and alower alkyl ester of an aromatic dicarboxylic acid.
 14. The developercomposition according to claim 13, wherein said aliphatic dicarboxylicacid is a member selected from the group consisting of maleic acid,fumaric acid, citraconic acid, itaconic acid, glutaconic acid, succinicacid, adipic acid, sebacic acid, azelaic acid, malonic acid,n-dodecenylsuccinic acid, isododecenylsuccinic acid, n-dodecylsuccinicacid, isododecyl succinic acid, n-octenylsuccinic acid, andn-octylsuccinic acid, and said aromatic dicarboxylic acid is a memberselected from the group consisting of phthalic acid, isophthalic acid,and terephthalic acid.
 15. The developer composition according to claim10, wherein said triol or higher polyol monomer is a member selectedfrom the group consisting of sorbitol, 1,2,3,6-hexanetetrol,1,4-sorbitan, pentaerythritol, dipentaerythritol, tripentaerythritol,1,2,4-butanetriol, 1,2,5-penatetriol, glycerol, 2-methylpropanetriol,2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane and1,3,5-trihydroxymethylbenzene.
 16. The developer composition accordingto claim 10, wherein said tricarboxylic or higher polycarboxylic acidmonomer is a member selected from the group consisting of1,2,4-benzenetricarboxylic acid, 2,5,7-naphthalenetricarboxylic acid,1,2,4-naphthalenetricarboxylic acid, 1,2,4-butanetricarboxylic acid,1,2,5-hexanetricarboxylic acid,1,3-dicarboxyl-2-methyl-2-methylenecarboxypropane,1,2,4-cyclohexanetricarboxylic acid, tetra(methylenecarboxyl)methane,1,2,7,8-octanetetracarboxylic acid, pyromellitic acid, enpole trimeracid, an anhydride of any one of the foregoing, and a lower alkyl esterof any one of the foregoing.
 17. The developer composition according toclaim 1, wherein said first polyester and said second polyester aremelt-blended with each other.
 18. The developer composition according toclaim 1, wherein said developer composition further contains a memberselected from the group consisting of an additive, a resin, a flowimprover, and a cleaning improver.
 19. The developer compositionaccording to claim 18, wherein said additive is a low molecular weightpolyolefin.
 20. The developer composition according to claim 19, wheresaid low molecular weight polyolefin is low molecular weightpolyethylene or polypropylene.
 21. The developer composition accordingto claim 20, wherein said low molecular weight polyethylene orpolypropylene has a softening point determined by the ring-and-ballmethod of 70° to 150° C.
 22. The developer composition according toclaim 21, wherein said low molecular weight polyethylene orpolypropylene has a softening point of 120° to 150° C.
 23. The developercomposition according to claim 1, wherein said colorant is at least onemember selected from the group consisting of carbon black, nigrosinedyes (C.I. No. 50415B), aniline blue (C.I. No. 50405), chalco oil blue(C.I. No. azoic Blue 3), chrome yellow (C.I. No. 14090), ultramarineblue (C.I. No. 77103), de Pont oil red (C.I. No. 26105), quinolineyellow (C.I. No. 47005), methylene blue chloride (C.I. No. 52015),phthalocyanine blue (C.I. No. 74160, malachite green oxalate (C.I. No.42000), lamp black (C.I. No. 77266), rose bengal (C.I. No. 45435), and amixture thereof.
 24. The developer composition according to claim 1,wherein said colorant is present in an amount of from 1 to 20 parts byweight per 100 parts by weight of said developer composition.
 25. Thedeveloper composition according to claim 24, wherein said developercomposition has a mean particle size of 3 to 30 μm.
 26. The developercomposition according to claim 18, wherein said flow improver is amember selected from the group consisting of silica, alumina, titaniumoxide, barium titanate, magnesium titanate, calcium titanate, strontiumtitanate, zinc oxide, quartz sand, clay, mica, wollastonite,diatomaceous earth, chromium oxide, cerium oxide, red iron oxide,antimony trioxide, magnesium oxide, zirconium oxide, barium sulfate,barium carbonate, calcium carbonate, silicon carbide, and siliconnitride.
 27. The developer composition according to claim 18, whereinsaid flow improver is impalpable powder of silica.
 28. The developercomposition according to claim 27, wherein said impalpable powder ofsilica is a fine powder of aluminum silicate, sodium silicate, potassiumsilicate, magnesium silicate, zinc silicate, or anhydrous silicondioxide.
 29. The developer composition according to claim 28, whereinsaid impalpable powder of silica contains 85 to 100% by weight of SiO₂.30. The developer composition according to claim 27, wherein saidimpalpable powder of silica is subjected to surface treatment with amember selected from the group consisting of a silane coupling agent, atitanium coupling agent, a silicone oil, and a silicone oil having anamine in its side chain.
 31. The developer composition according toclaim 18, wherein said cleaning improver is an impalpable or fine powderof a metal salt of a higher fatty acid or a fluoropolymer.
 32. Thedeveloper composition according to claim 31, wherein said metal salt ofa higher fatty acid is zinc stearate.
 33. The developer compositionaccording to claim 18, wherein said additive is an additive foradjusting developability.
 34. The developer composition according toclaim 33, wherein said additive is an impalpable powder of a polymer ofmethyl methacrylate.
 35. The developer composition according to claim18, wherein said additive is carbon black.
 36. The developer compositionaccording to claim 35, wherein said carbon black is a member selectedfrom the group consisting of furnace black, channel black, and acetyleneblack.